Microbiolgoically-defined laboratory animals are required for sophisticated biomedical research. Serological procedures are the most feasible and economical means to monitor their health status. Tyzzer's disease is one of the more insidious diseases of laboratory rodents and rabbits for which a serologic test procedure is not available commercially. The elusive fastidious etiologic agent, Bacillus piliformis (N.SP., Tyzzer), parasite which remains unclassified. Typical histopathology forms the basis for diagnosis in 18 animal species. Immunosuppression precipitates clinical disease. Transmission occurs vertically as well as horizontally. Serological surveys in Japan and Europe indicate that inapparent infections are common in cesarean-derived, barrier-maintained colonies of rats. Microbiological Associates, Inc. proposes to prepare seed pools of 5 strains of B. piliformis (propagated in embryonated eggs and primary hepatocyte cell cultures), prepare antisera to each strain in mice and rats, adapt the ELISA and IFAT techniques for serodiagnosis, determine the degree of antigenic relatedness between strains, and provide serodiagnostic services to the biomedical research community at reasonable cost.